Effects and modes of action of citrus limonoids against Leptinotarsa decemlineata

Limonin and its five derivatives were evaluated in feeding bioassays for depression effects on feeding, growth and development of the fourth stadium Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Epilimonol and limonin diosphenol were most effective in depression of feeding and growth, with ED 50 s 10 and 8 μg/cm 2 . At a dosage of 31.6 μg/cm 2 , epilimonol, limonin diosphenol and limonin caused both significant feeding reduction and developmental delay, while deoxylimonol, tetrahydrolimonin and limonol were not effective. Mouth‐part coating and antifeedant bioassays show that feeding inhibition at host acceptance level seems to be the primary mode of action of epilimonol and limonin diosphenol.